[PATCH] D81988: [ELF] Fix a dyn_cast<Defined>(nullptr) crash if a local symbol appears in InputFile::symbols

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, jhenderson, psmith.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

Fixes PR46348

InputFile::symbols normally contains non-local symbols. A broken .symtab
may have a local symbol whose index is >= sh_info. In this case, we
store a nullptr in InputFile::symbols. Use dyn_cast_or_null instead of
dyn_cast to avoid a crash.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81988

Files:
  lld/ELF/InputSection.cpp
  lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test


Index: lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test
===================================================================
--- /dev/null
+++ lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test
@@ -0,0 +1,28 @@
+# REQUIRES: x86
+## Test that we check nullptr entries in InputFile::symbols (which is supposed to be a
+## non-local symbol list). `local` is a nullptr entry.
+
+# RUN: yaml2obj %s -o %t.o
+# RUN: not ld.lld %t.o %t.o -o /dev/null 2>&1 | FileCheck %s
+# CHECK:      error: duplicate symbol: _start
+# CHECK-NEXT: >>> defined at {{.*}}.o:(.text+0x0)
+# CHECK-NEXT: >>> defined at {{.*}}.o:(.text+0x0)
+
+!ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  OSABI:   ELFOSABI_FREEBSD
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Type:    SHT_PROGBITS
+    Name:    .text
+    Flags:   [ SHF_ALLOC, SHF_EXECINSTR ]
+Symbols:
+  - Name:     _start
+    Section:  .text
+    Binding:  STB_GLOBAL
+  - Name:     local
+    Section:  .text
+    Binding:  STB_LOCAL
Index: lld/ELF/InputSection.cpp
===================================================================
--- lld/ELF/InputSection.cpp
+++ lld/ELF/InputSection.cpp
@@ -347,7 +347,7 @@
 
   // Find a symbol that encloses a given location.
   for (Symbol *b : file->getSymbols())
-    if (auto *d = dyn_cast<Defined>(b))
+    if (auto *d = dyn_cast_or_null<Defined>(b))
       if (d->section == this && d->value <= off && off < d->value + d->size)
         return filename + ":(" + toString(*d) + ")" + archive;
 


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